This invention relates to a process for the isolation of polyols from a fermentation source. Specifically, this invention relates to a process for the isolation of 1,3 propanediol from a fermentation source.
Polyols are compounds that contain two or more hydroxyl groups. 1,3-Propanediol is one example of a polyol. 1,3-Propanediol is a precursor for several polymeric materials including polyether polyols, polyester homopolymers and copolymers, and thermoplastic elastomers. 1,3-Propanediol is commercially produced via chemical synthesis routes including (a) ethylene oxide hydroformylation followed by hydrogenation, and (b) hydration of acrolein followed by hydrogenation. Both routes rely on petroleum based feedstocks. Purification of petroleum-based 1,3-propanediol requires significant effort as the quality of the aforementioned polymeric products is generally dependent on the quality of the monomers.
Alternatively, 1,3-propanediol can be produced from processing of renewable agricultural resources which yield fermentable sugars, especially glucose. Glucose can be converted to 1,3-propanediol via a single biocatalyst, yielding an aqueous fermentation broth containing many residual medium components and byproducts. Fermentation residuals and byproducts are in general different from impurities found in chemical synthesis. Inherent in biological systems utilizing agricultural feedstocks, is greater variability in composition of product than obtained with chemical synthesis from petroleum feedstocks. Furthermore, fermentation residuals and byproducts in general encompass a wider range of structures and physical properties than chemical synthesis byproducts. Isolation and purification of 1,3-propanediol from a fermentation source therefore has significant and unmet challenges above that of processes which produce 1,3-propanediol via chemical synthesis.
U.S. Pat. No. 5,527,973 discloses a process for purifying a carbonyl-containing 1,3-propanediol composition. The process involves formation of an acidic aqueous medium, addition of a base to raise the pH to greater than 7, distillation of the solution to remove water, and subsequent distillation of the 1,3-propanediol yielding a product with lower carbonyl content than the starting composition. This disclosure does not address 1,3-propanediol produced via a fermentation process, nor byproducts and impurities specific to a fermentation process, nor byproducts formed during isolation and purification of such a material. Examples outside the scope of this disclosure include organic acids, proteins, inorganic salts, lactones, nitrogen heterocycals, and color bodies.
Separation and purification of chemicals produced by fermentation are driven both by the nature of the product and the nature of a typical fermentation broth. Fermentations may typically produce a broth which contains only a 1 to 10% concentration of the desired product. Furthermore, the broth contains biomass and a wide variety of other constituents potentially including but not limited to: proteins, amino acids, lipids, organic acids, organic and inorganic salts, and residual medium nutrients. Two common steps in processing of broth are therefore removal of biomass, and isolation of the product from the highly dilute system. Biomass removal may typically be done by filtration or centrifugation. A wide variety of isolation methods are available including filtration, evaporation, extraction, and crystallization. After isolation step(s), the product may be expected to be the major component, with impurities comprising a smaller fraction of the composition. If deemed necessary, purification involves removal of impurities to the degree required for an acceptable product.
Barantsev et al. (Fermentn. Spirt. Prom-st. 2:24-27 (1976)) disclose a method for reducing the quantities of impurities formed and improving distillate quality in alcohol distillation. The distillation feed was molasses fermented mashes, which was reported to produce impurities from interaction of alcohols, acids, aldehydes, and amino acids. Improvements were made by raising pH, and reducing the pressure and therefore the distillation temperature. This study does not address the conditions required for processing polyols in general, and more specifically 1,3-propanediol. Atmospheric distillation of ethanol and 1,3-propanediol would occur at 78 and 214xc2x0 C., respectively. While distillation at a vacuum of 50 mmHg would reduce the ethanol distillation to 22xc2x0 C., and 1,3-propanediol distillation would operate at 137xc2x0 C. Therefore, the energy available for reaction activation is significantly different and greater for 1,3-propanediol processing. Barantsev does not consider glycol dehydration reactions, or more specifically 1,3-propanediol dehydration reactions. In addition, Barantsev does not consider a process where water is removed as a vapor, and the product which has a higher boiling point remains in the liquid phase as xe2x80x9cbottomsxe2x80x9d or xe2x80x9cheelxe2x80x9d. The process does not address abatement of impurities which are either known or believed to be unique to 1,3-propanediol processing. Furthermore, Barantsev does not disclose a pH which is optimal for processing 1,3-propanediol produced by fermentation or consider color of purified 1,3-propanediol.
A method to isolate polyols produced by fermentation processes without the deficiencies discussed above remains a problem to be solved. More specifically, a process for the isolation of 1,3-propanediol from fermentation is needed.
The present invention discloses a process for the isolation of polyol(s) from a fermentation broth comprising the steps of:
(a) adding base to the fermentation broth to raise the pH to at least 7.0; and
(b) isolating the polyol from the fermentation broth of step (a).
Polyols of particular interest in the invention are 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, glycerol, or ethylene glycerol. Isolating in step (b) is by evaporating, distilling, filtering, extracting, or crystallizing. After step (c) the invention may further include removing precipitated solids from the product of step (b) by 1) filtering or centrifuging, or 2) vacuum distilling.